The present invention relates to a drive device for an electric motor.
The German patent document DE 42 38 375 A1 discloses a drive device, for example for moving a movable roof of a vehicle. The drive device includes an electric motor with a rotor which drives a rotor shaft in two rotary directions, and for example a screw transmission driveable by the rotor shaft, a pole on the motor shaft, as well as a hall sensor oriented toward the pole wheel so that when the pole wheel is rotated by the motor shaft, signals are supplied to an evaluating circuit.
The patent document WO 91/091 98 discloses a further drive device, whose permanent magnet is formed as a ring of a magnetizable material and is magnetized so that it has in its periphery a north pole and a south pole. A magnetizing process which is needed for forming the north pole and the south pole is possible technically in a simple manner. Two hall sensors are associated with this permanent magnet and arranged at an angular distance of 90.degree. around the rotary axis. Thereby an evaluating device can determine also the rotary direction in addition to the number of revolutions, from a sequence of signals from both hall sensors. This drive device is used for driving a window lifter, a displacing roof carrier, a mirror adjuster and the like in the vehicle.